1. Field of the Invention
This invention relates to a system for construction of an overcast for use in a mine. In coal mines it is usual to form a network of spaced apart passageways separated by pillars. Some of the passageways are utilized to provide ventilation to the active mining faces while others are utilized to provide a ventilation return path from the face. Cross passages communicating between the ventilation passageways are generally closed in order to improve ventilation flows.
2. Description of the Prior Art
In large passageways closing of cross passages is achieved by providing an overcast that is to say an arch like framework which permits passage through the arch and which is capable of supporting a wall or partition extending from the overcast up to the mine roof. In the past the overcast has been constructed from angle iron carried into the mine and bolted together to form the frames. A typical steel overcast required three to four hundred bolts for assembly and involves four men for four shifts for completion. The components are relatively heavy and difficult to handle in confined space within the mine.
In addition, mine passages are not of uniform dimension, nor of uniform cross-section, and in fact are liable to change in cross-section due to floor heave or roof pressure. Therefore prior overcasts built to suit the dimensions of a mine passage can be structurally deformed and/or damaged by floor heave or roof pressure.